The present invention relates to apparatus and methods for energy storage and, more particularly, apparatus and methods for permitting in-situ determination and utilization of the state of charge and state of health of storage components in a microgrid.
Microgrids are rapidly expanding as part of the effort to reduce dependence on fossil fuels and to increase the efficiency of generating electric energy. The microgrids typically consist of power generators, renewable energy sources and energy storage components. For energy storage, components such as rechargeable batteries, super-capacitors, fuel-cells, and the like, are used. One of the main objectives of the microgrids is to effectively use the electric storage to maintain line voltage regulation which can mainly occur due to the unpredictable duty cycles of the renewables. In order to lower the mass, volume and cost of each energy storage components and for microgrid life cycle cost reduction, it is essential that the stored energy is expended and restored efficiently while maximizing energy storage component operational life.
Conventional energy storage component charge/discharge control is based upon terminal voltage monitoring and the labeled component capacity values. The terminal voltage, particularly in the dynamic charge/discharge environment of the electric grid, is not a true indicator of storage component state of charge and can result in overcharge or overdischarge of the device. Further, the component capacity fades with time and, if the component utilization is not based upon its current capacity, premature wear and system failure can result.
As can be seen, there is a need for methods and apparatus for effective utilization of diverse types of energy storage components with a microgrid based upon their state of charge and state of health.